Correct few typos and rephrase

Co-authored-by: Lukas Riedel <[email protected]>

Author: luseverin

doc/guide/Guide_Euler.ipynb

@@ -194,9 +194,9 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### 7. Optional: install Climada Petals\n",
+    "### 7. Optional: Install Climada Petals\n",
     "\n",
-    "To install Climada Petals, repeat the steps described in step 4 as option A, but replacing the climada_python with the climada_petals repository:\n",
+    "To install Climada Petals, repeat the steps described in step 4A, but replacing the climada_python with the climada_petals repository:\n",
     "```bash\n",
     "cd /cluster/project/climate/$USER  # or wherever you plan to download the repository\n",
     "git clone https://github.com/CLIMADA-project/climada_petals.git  # unless this has been done before\n",